The incidence of incidental renal masses has increased significantly due to frequent use of abdominal imaging. Simple renal cysts are common in the population. Four-to-seven percent of the renal cancers arise from cystic masses. Today, Bosniac classification is used for evaluation of renal cysts regarding the risk of malignancy. The most significant drawback of Bosniac Classification is its lack of ability to distinguish category III cysts from the category II cysts. Renal biopsy is an effective and efficient diagnostic procedure with 90% sensitivity, 92% specificity, 95% positive predictive value and 80% negative predictive value for cancer, reported in contemporary series. The technique of percutanous renal biopsy has improved in the last 2 decades. The potential complications include: hematomas, massive hematuria, arteriovenous fistulae and tumor seeding in the needle tract. Lack of sufficient amount of tissue to achieve a proper diagnosis is another unwanted situation. Today there is not a better diagnostic tool than biopsy when imaging is not helpful in distinguishing malignant lesions from the benign ones.